The invention relates to an apparatus for ultrasonic scanning comprising an ultrasonic applicator which, by means of a plurality of individual transducer elements, is designed for the transmission of ultrasonic signals and for the reception of the echo signals, and wherein at least in the electric receiving circuit, a delay device chronologically delays the incoming echo signals for each transducer element such that there results, in the chronological sequence of the arrival of signals at the individual elements, phase balance of the individual signals at the summation circuit connected with the output of the delay device.
An apparatus of this type is, for example, described in an article in "Ultrasonics Symposium Proceedings", IEEE CAT. 1977, at pages 250 to 254. This apparatus operates in analog or digital technique with storage members as a delay network, wherein a common summing amplifier is activated by the storage members. In addition, it has already been proposed in German patent application No. P 29 42 049.3 (U.S. Ser. No. 191,779 filed Sept. 29, 1980, now U.S. Pat. No. 4,373,395 issued Feb. 15, 1983) to sequentially digitally store ultrasonic signals arriving at the individual transducers, whereby, in particular, the possibility of an optimized signal processing results.
In the case of apparatus of the type initially cited, a number m of individual transducer elements each of a width b form an array of the overall width B. As a whole, such a transducer array can be employed, for example, for phase-controlled array systems in the case of ultrasonic apparatus with sector scanning by means of an electronic beam pivoting, whereby additionally also a dynamic focusing is possible. In addition to this, the utilization in the case of a linear array without beam pivoting, but with dynamic focusing, is conceivable. In all cases, a good resolution is desired. If the width b of an individual transducer element is greater than the wavelength of the ultrasonic signals emitted by the array, however, as is known, so-called "grating lobes" occur in the directional sensitivity (or response) of the array, which grating lobes considerably impair the lateral resolution. For this reason, one seeks to increase the number of transducer elements in the specified aperture range as far as possible, as a consequence of which the width b of an individual element must be correspondingly reduced. In the case of the phase-controlled array systems, however, the outlay for a controlling electronic system with preamplifiers, delay lines and the like, is thereby increased in an undesired manner, so that other solutions are sought for.